ISL6557A 查看數據表（PDF） - Renesas Electronics
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ISL6557A Datasheet PDF : 18 Pages
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ISL6557A
Application on page 3). Figure 14 and Equation 26 are
0.3
provided to assist in the selecting the correct value for RT.
1000
0.2
100
10
10
100
1000
SWITCHING FREQUENCY (KHZ)
FIGURE 14. RT VS SWITCHING FREQUENCY
10000
RT = 1011.09 – 1.13log fS
(EQ. 26)
Input Capacitor Selection
The input capacitors are responsible for sourcing the ac
component of the input current flowing into the upper
MOSFETs. Their rms current capacity must be sufficient to
handle the ac component of the current drawn by the upper
MOSFETs which is related to duty cycle and the number of
active phases.
Figures 15, 16 and 17 can be used to determine the input-
capacitor rms current as of duty cycle, maximum sustained
output current (IO), and the ratio of the combined peak-to-peak
inductor current (IL,PP as defined in Equation 1) to the
maximum sustained load current, IO. Figure 18 is provided as
a reference to demonstrate the dramatic reductions in input-
capacitor rms current upon the implementation of the
multiphase topology.
0.1
IL,PP = 0
IL,PP = 0.5 IO
IL,PP = 0.75 IO
0
0
0.2
0.4
0.6
0.8
1.0
DUTY CYCLE ( VIN / VO )
FIGURE 15. NORMALIZED INPUT-CAPACITOR RMS
CURRENT VS DUTY CYCLE FOR 2-PHASE
CONVERTER
0.3 IL,PP = 0
IL,PP = 0.25 IO
IL,PP = 0.5 IO
IL,PP = 0.75 IO
0.2
0.1
0
0
0.2
0.4
0.6
0.8
1.0
DUTY CYCLE ( VIN / VO )
FIGURE 16. NORMALIZED INPUT-CAPACITOR RMS
CURRENT VS DUTY CYCLE FOR 3-PHASE
CONVERTER
FN9068 Rev 3.00
July 2004
Page 16 of 18
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